diff --git a/pyjs_code_runner/backend/browser_main/browser_main.py b/pyjs_code_runner/backend/browser_main/browser_main.py
index 240ee4b..88d1a74 100644
--- a/pyjs_code_runner/backend/browser_main/browser_main.py
+++ b/pyjs_code_runner/backend/browser_main/browser_main.py
@@ -75,7 +75,7 @@ async def handle_console(msg):
                         collected_prints += "\\n";
                     }}
 
-                    var pyjs = await make_pyjs(print,print);
+                    var pyjs = await make_pyjs(print,print, true);
 
                     var r = globalThis.eval_main_script(pyjs, "{self.work_dir}","{self.script}");
                     if({int(self.async_main)}){{
diff --git a/pyjs_code_runner/backend/browser_worker/browser_worker.py b/pyjs_code_runner/backend/browser_worker/browser_worker.py
index 1a9d527..1e7a965 100644
--- a/pyjs_code_runner/backend/browser_worker/browser_worker.py
+++ b/pyjs_code_runner/backend/browser_worker/browser_worker.py
@@ -10,7 +10,7 @@
 
 class BrowserWorkerBackend(BackendBase):
     def __init__(
-        self, host_work_dir, work_dir, script, async_main, port, headless, slow_mo
+        self, host_work_dir, work_dir, script, async_main, port, headless, slow_mo, preload_shared_libs=True
     ):
         super().__init__(
             host_work_dir=host_work_dir,
@@ -23,6 +23,7 @@ def __init__(
         self.port = port
         self.headless = headless
         self.slow_mo = slow_mo
+        self.preload_shared_libs = preload_shared_libs
 
     def run(self):
         # copy html
@@ -73,7 +74,7 @@ async def handle_worker(worker):
                     }}
 
 
-                    var pyjs = await make_pyjs(print, print);
+                    var pyjs = await make_pyjs(print, print, {str(self.preload_shared_libs).lower()});
 
                     var r = eval_main_script(pyjs, "{self.work_dir}","{self.script}");
                     if({int(self.async_main)}){{
diff --git a/pyjs_code_runner/js/utils.js b/pyjs_code_runner/js/utils.js
index 4adb5c6..f576f62 100644
--- a/pyjs_code_runner/js/utils.js
+++ b/pyjs_code_runner/js/utils.js
@@ -17,13 +17,14 @@ async function fetchMounts(pyjs) {
 
 }
 
-async function make_pyjs(print, error) {
+async function make_pyjs(print, error, preload_load_shared_libs=true) {
     var pyjs = await createModule({ print: print, error: print })
 
    await pyjs.bootstrap_from_empack_packed_environment(
         `./empack_env_meta.json`, /* packages_json_url */
         ".",               /* package_tarballs_root_url */
-        false              /* verbose */
+        false,              /* verbose */
+        !preload_load_shared_libs  /* skip_loading_shared_libs */
     );
     globalThis.pyjs = pyjs
     return pyjs
diff --git a/test/conftest.py b/test/conftest.py
index 607a0f8..790af44 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -57,5 +57,5 @@ def em_work_dir():
 
 @pytest.fixture
 def runner():
-    runner = CliRunner(mix_stderr=True)
+    runner = CliRunner()
     return runner